The present invention relates to a method of grinding the work rolls of a planetary rolling mill and to a device for carrying out such method.
Planetary rolling mills have been known for many years. One embodiment thereof is described in U.S. Pat. No. 3,333,452. Such rolling means can be used to advantage in the manufacture of material in strip form for small and medium quantity production. Despite a large number of advantages in the manufacture of steel strip, they have not been widely used up to now in the production operations of the steel industry. One of the reasons for this--perhaps the main reason--is that the time required for changing and regrinding the required work rolls is rather long, a fact which, in view of the short service life wherein the work rolls are so worn after about six hours that they must be reground, is particularly important. The advantages of a planetary rolling mill with regard to low operating expense and low capital requirement are therefore opposed by the disadvantages of higher maintenance costs as compared with conventional rolling mills.
A typical planetary rolling mill includes two planet rolls, which in the sense used here, each comprises two chocks, a support body, two cages, and for instance 24 work rolls as well as 24 intermediate rolls. When the work rolls have been worn down to such an extent that they must be reground, the two planet rolls which are in use at the time are replaced by new work rolls, i.e. reground, or entirely new, work rolls. Such a replacement of planet rolls is possible in about 10 minutes, so that the rolling process is not greatly impaired thereby.
The planet rolls, which weigh about 100 tons each, are transported, after removal from the stand, to an assembly place where the work rolls (2.times.24 rolls) are removed by hand. The intermediate rolls have a substantially longer life; they need be reworked only about every 20th time; in the normal case, therefore, they remain in the planet roll. The work rolls, after grinding of the individual rolls in a grinding device, are reinstalled by hand into the planet rolls.
Solely for the removal and reinstalling of the 48 work rolls of a roll stand for a rolling width of 1300 mm, about 12 hours work on the part of a mechanic is necessary, which, with a life of the work rolls of about 6 hours, constitutes a considerable cost factor.
An object of the present invention is to substantially reduce the time and expense for the necessary regrinding of the work rolls of a planetary rolling mill.
The foregoing object is achieved in a manner for grinding the work rolls of a planetary rolling mill wherein a complete planetary roll with cages and chocks is removed from a roll stand and clamped in a grinding device having a grinding wheel; and the work rolls are then ground, one after the other, in an installed condition in a manner such that the cages of the work rolls are fixed in each case in the grinding position for a specific work roll, with the corresponding work roll being moved radially outward so far that it can turn freely with respect to the corresponding intermediate roll and to the work roll being machined by corresponding multiple infeed and longitudinal movements of the grinding wheel; and then the complete planet roll is reinstalled into the roll stand after grinding.
In this method, the large amount of labor that was previously necessary for the removal, transportation to a grinding machine, and reinstalling of the work rolls is avoided. A complete planet roll, after removal from the roll stand, is transported to a special grinding device and clamped in it, and the work rolls are then ground one after the other in an installed condition. For this purpose, the cages in each case are turned by one roll spacing so that a work roll is precisely at the height of the center of the grinding wheel or somewhat below same, in which connection, by positioning somewhat below the same, a "pulling in" is reliably avoided even in unfavorable cases. In this position, the cages are stopped and the work roll to be ground is moved radially outward by a special device so that it no longer is in contact with the corresponding intermediate roll. The grinding wheel, which is located on the one side of the grinding device and possibly somewhat to the side of the work roll, is moved inward, i.e. as far in the direction of the work roll as is necessary for the first grinding operation, and then moved along the work roll. After another infeed on the opposite end of the work roll the next grinding operation takes place in opposite direction. This is repeated until a predetermined amount of removal or roll diameter has been reached. The grinding wheel is then moved backward, and the next work roll brought into grinding position and ground until all work rolls have been taken care of.
In order to assure a dependable grinding of the work rolls, it is necessary that they be turned during the grinding process. Various possibilities for this are conceivable. However, it is of particular advantage to turn the work roll by means of a separate friction roller having a drive of its own, preferably in a direction opposite the direction of rotation of the grinding wheel. After the friction roller has been swung into working position and the drive connected, i.e. the work roll is rotating, the grinding wheel is advanced and then moved along the work roll. Due to the special arrangement of a drive rocker in the form of a bracket arm and a rocker, an uninterrupted driving of the work roll to be ground is assured during the entire grinding process, as well as an unimpeded movement of the grinding wheel over the entire length of the work roll. It may be advantageous to use two friction rollers instead of a single one in order to achieve a dependable driving of the work rolls under even difficult conditions.
In accordance with a further development of the invention, the rotation of the cages and the radial displacement of the work rolls is effected by means in or on the cages themselves. For this purpose, the cages are provided with an outer toothing the pitch of which agrees with that of the work roll or is in the ratio thereto of a fraction having a whole-number denominator. The drive is effected by a relatively small drive motor independently of the drive of the grinding wheel. The radial displacement for lifting the work roll off from the corresponding intermediate roll is effected with particular advantage by a respective cylinder bore that is present under each spring package in the cages and a piston which is moveable therein. Through a feed bore, the space below the piston corresponding to the work roll to be ground is acted upon by pressure. In this way, the piston comes against the spring package, the latter is compressed and the work roll is thus moved radially outward and lifted off from the intermediate roll. The work-roll chocks come against adjustable fixed stops on the grinding machine and are clamped in a forced-locked manner in this position by the cylinders. The feed bores are provided on the outer mouths of the cage with quick-closure couplings so that, in each case, only the two feeds (right and left) of the work roll that are just about to be worked are connected, and the change in connection for the next work roll takes place very rapidly.
For the clamping of the work roll on the grinding device, the chocks are provided with grooves into which corresponding clamping elements or sliding blocks engage. The clamping elements or sliding blocks are pulled in by tie rods and hydraulic cylinders, thus pulling the chocks firmly against the clamping pedestals of the grinding device.
For an easy, time- and cost-saving grinding of work rolls of a planetary rolling mill, a complete planet roll with cages and chocks is removed from a roll stand and clamped in a grinding device having a grinding wheel. The work rolls are ground in an installed condition, one after the other, in a manner wherein (i) cages of the work rolls are in each case held fast in a grinding position for a specific work roll, (ii) the corresponding work roll is removed radially outward so far that it can turn freely with respect to a corresponding intermediate roll, and (iii) the work roll is machined by a corresponding multiple infeed and longitudinal movements of the grinding wheel. The complete planet roll is reinstalled in the roll stand after grinding. In such method, the grinding device used comprises a clamping pedestal for fixing in position the chocks, a compound slide for the grinding wheel, an indexing device for turning the cages, and a locking device, the foregoing items being arranged on a foundation plate or frame; and a bracket arm having a drive device with a friction roller for turning the work rolls which arm is firmly connected to, or directly alongside, the foundation plate or frame. The planetary roll is placed with its chocks on the foundation plate or foundation frame, possibly with interposed spacer plates. The clamping pedestal is connected to the foundation plate or foundation frame on one side and to the compound slide on the other side. The clamping pedestal is possibly adapted to be displaced and fixed in place by suitable fastening elements so as to permit adaptation to planet rolls of different diameter. The grinding wheel together with its drive is arranged on the compound slide. The infeed movement of the grinding wheel and its movement along the work roll are effected by means of this compound slide. The bracket arm having a drive device with a friction roller is firmly attached to, or directly alongside, the foundation plate or foundation frame. Furthermore, the grinding device has, between the clamping pedestal and the compound slide, a turning device provided with two pinions and two stop means that engage into the outer toothing of the cages.
One particularly advantageous development of the grinding device of the invention consists in arranging the drive device with a friction roller for driving the work roll as a rocker with an integrated gearing. This rocker is turnably supported on the upper end of the bracket arm facing the planetary roll. This mounting is provided, for the exact positioning of the friction roller (i.e. for the readjustment for the individual grinding steps) with an eccentric bushing. The other end of the rocker opposite the friction roller is acted on by a hydraulic cylinder by which the friction roller is swung, after the radial travel of the work roll to be machined, in such a way in the direction towards the planet roll that it comes to lie on the work roll to be ground and drives the latter. The friction roller is driven by a drive motor arranged on the rocker via a gearing integrated in the rocker. This friction drive is fixed in space while the grinding carriage bearing the grinding wheel carries out an oscillating movement.
The method of the invention for the grinding of work rolls of a planetary rolling mill and the apparatus necessary for this as well as the required structural development of the planet rolls are shown, for instance, in the accompanying FIGS. 1 to 5 and will be described in further detail below. Structural details with which the person skilled in the art will be acquainted have been omitted for ease in understanding the drawing.